1. Field of the Invention
The present invention relates to a hydraulic engine-starting system for starting an engine for a vehicle having automatic stopping and starting functions by cranking the engine using a hydraulic motor.
2. Related Art
Automatic engine-stopping and starting systems are known from Japanese Patent Application Laid-open Nos. 8-14076 and 2000-46165. They are designed so that when a vehicle is stopped during traveling and predetermined conditions are established, the engine is stopped automatically. Likewise, when an accelerator pedal is depressed to start the vehicle, the engine starts automatically, thereby saving fuel and reducing exhaust emission.
A hydraulic pressure that operates a hydraulic clutch of a transmission is generated by an oil pump driven by the engine. For this reason, when the engine is stopped upon stopping the vehicle, the oil pump also stops. Therefore, even if the engine is started at the start of the vehicle to drive the oil pump, it is difficult to immediately raise the hydraulic pressure required to operate the hydraulic clutch of the transmission. Raising of the hydraulic pressure for the transmission is retarded for this reason. Thus, the hydraulic clutch is brought into engagement after increasing the rotational speed of the engine, a shock is then generated by the engagement of the hydraulic clutch, and smooth starting of the vehicle is not possible.
In order to avoid this, the automatic engine-stopping and starting system described in Japanese Patent Application Laid-open No. 8-14076 includes a large-sized accumulator in which a hydraulic pressure is accumulated by an oil pump driven by the engine. In this system, a working oil is supplied from the accumulator to the transmission at the start of the engine to ensure a hydraulic pressure required for the engagement of the hydraulic clutch. The automatic engine-stopping and starting system described in Japanese Patent Application Laid-open No. 2000-46165 includes an electric oil pump separate from an oil pump driven by the engine so that the hydraulic clutch of the transmission is operated by a hydraulic pressure generated by the electric oil pump at the start of the engine when the oil pump driven by the engine cannot generate a sufficient hydraulic pressure.
An automatic engine-stopping and starting system is also known from Japanese Patent Application Laid-open No. 6-101606, which is designed so that a lubricating oil is supplied to portions of an engine, which are to be lubricated, by an electric hydraulic pump prior to the start of the engine, thereby preventing the portions from being abnormally worn at the start of the engine.
However, the automatic engine-stopping and starting system described in Japanese Patent Application Laid-open No. 8-14076 requires the large-sized accumulator, and the automatic engine-stopping and starting system described in Japanese Patent Application Laid-open No. 2000-46165 requires the electric oil pump. Therefore, these systems suffer from increased cost, energy consumption, and battery consumption.
It is an object of the present invention to ensure that the hydraulic pressure for operating the hydraulic clutch of the transmission and/or the hydraulic pressure for lubricating the engine is raised promptly by using a hydraulic motor to start the engine.
For example, a hydraulic engine-starting system can be provided in a vehicle and include an engine and a transmission that transmits an output from the engine to driven wheels in a speed-changing manner. A hydraulic pressure source generates a hydraulic pressure, while an accumulator accumulates the hydraulic pressure generated thereby. A hydraulic motor starts the engine and a first oil passage supplies oil from the accumulator to the hydraulic motor while a second oil passage returns the oil from the hydraulic motor to the hydraulic pressure source. Oil flowing through the second oil passage is used as a working oil for the transmission and/or a lubricating oil for the engine.
With the above arrangement, the hydraulic motor can be driven by the oil supplied thereto from the accumulator via the first oil passage and the engine cranked and started by a driving force generated by the hydraulic motor. Since the oil discharged from the hydraulic motor maintains a sufficient hydraulic pressure and the transmission and/or engine is disposed at an intermediate portion of the second oil passage, the oil can be used as the working oil for the transmission and/or the lubricating oil for the engine. Therefore, the hydraulic pressure in the transmission can be raised simultaneously with the start of the engine by the hydraulic motor, thereby starting the vehicle without generating any shock due to the engagement of the hydraulic clutch. Alternatively or concurrently, portions of the engine, which are to be lubricated, can be lubricated simultaneously with the start of the engine by the hydraulic motor, to thereby prevent abnormal wear.
The hydraulic engine-starting system can also include a third oil passage that circulates the oil between the transmission or the engine and an oil cooler, wherein at least one portion of the third oil passage also serves as at least one portion of the second oil passage.
With the above arrangement, since at least one portion of the third oil passage also serves as at least one portion of the second oil passage, the length of the second oil passage is minimized.
Another aspect of the hydraulic engine-starting system is an oil pump driven by the hydraulic motor, wherein the oil supplied from the oil pump is used as a working oil for the transmission and/or a lubricating oil for the engine.
With the above arrangement, the hydraulic motor can be driven by the oil supplied thereto from the accumulator via the first oil passage and the engine cranked and started by a driving force generated by the hydraulic motor. In addition, the oil supplied from the oil pump is used as the working oil for the transmission and/or as the lubricating oil for the engine. Therefore, the hydraulic pressure in the transmission can be raised simultaneously with the start of the engine by the hydraulic motor, to thereby start the vehicle without generating shock due to the engagement of the hydraulic clutch. Alternatively or concurrently, portions of the engine, which are to be lubricated, can be lubricated simultaneously with the start of the engine by the hydraulic motor, to thereby prevent abnormal wear.
According to yet another aspect of the hydraulic engine-starting system, an oil supply device can be operated by the oil flowing through the first oil passage, wherein the oil supplied from the oil supply device is used as a working oil for the transmission and/or a lubricating oil for the engine.
With the above arrangement, the hydraulic motor can be driven by the oil supplied thereto from the accumulator via the first oil passage and the engine cranked and started by a driving force generated by the hydraulic motor. In addition, the oil supplied from the oil supply device is used as the working oil for the transmission and/or as the lubricating oil for the engine. Therefore, the hydraulic pressure in the transmission can be raised simultaneously with the start of the engine by the hydraulic motor, to thereby start the vehicle without generating shock due to the engagement of the hydraulic clutch. Alternatively or concurrently, portions of the engine, which are to be lubricated, can be lubricated simultaneously with the start of the engine by the hydraulic motor, to thereby prevent abnormal wear.
Moreover, a reservoir for the transmission can also be used as a reservoir for the hydraulic pressure source.
With the above arrangement, the reservoir for the transmission is also used as the reservoir for the hydraulic pressure source and hence, it is unnecessary to mount a separate reservoir in the hydraulic pressure source, leading to a reduction in number of parts.
Furthermore, an oil pump can be used as the hydraulic pressure source in the present invention.